1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and a power-supply voltage adaptive control system. In particular, the present invention relates to a semiconductor integrated circuit having a flip-flop performing a low voltage operation and a power-supply voltage adaptive control system.
2. Description of Related Art
In recent years, the amount of development in an “extremely low power circuit” as a measure against global warming has been increasing. The extremely low power circuit is a semiconductor integrated circuit operating with an extremely low voltage about 0.5 V, with which power consumption can be greatly reduced. However, to reduce the operation voltage of the semiconductor integrated circuit causes several problems.
For example, when an operation voltage of a logic circuit is reduced, malfunction of a flip-flop included in the logic circuit may be caused. More specifically, the reduction in the operation voltage may cause “DC error” where an output value of the flip-flop is fixed to “0” or “1”. Also, the reduction in the operation voltage may cause “AC characteristics error” where AC characteristics such as latch characteristics and delay characteristics of the flip-flop become inadequate.
In a case where such the DC error and AC characteristics error occur randomly at a low frequency, “redundancy technique” is effective. More specifically, a redundant flip-flop is provided in a logic circuit and an error flip-flop where the DC error or the AC characteristics error occurs is replaced by the redundant flip-flop. Such the redundancy technique for flip-flop is disclosed, for example, in Non-Patent Literature 1 and Non-Patent Literature 2.